First stage pressure regulators of the above type are known in the art. The overpressure that may build up in the balance chamber is relieved thanks to the tubular shape of the force transfer stem between the first and the second movable walls which sealingly separate the balance chamber from the low pressure gas chamber and the ambient exposed chamber respectively. A hole in the tubular wall puts in communication the inside of the tubular stem with the balance chamber, whereas a pressure relief valve is provided at the end for connection to the second movable wall which separates the balance chamber from the ambient exposed chamber, which valve is a one-way valve or a check valve whose shut-off direction corresponds to a flow direction from the ambient exposed chamber to the balance chamber.
A valve of this type is known, for example, from U.S. Pat. No. 5,097,860.
The provision of a balance chamber having means for transferring force to the regulating valve element between the high pressure gas chamber and the low pressure gas chamber, which force transfer means are two movable walls rigidly interconnected by the intermediate stem and a force transfer extension connected to the regulating valve element allows to adapt the pressure regulating valve calibration to ambient pressure conditions.
The first and the second movable walls generally consist of combinations of pistons cooperating with elastically deformable diaphragms, and elastic means are generally further provided for adjusting a certain preload on said movable walls, and operating in the same direction as the force exerted by ambient pressure.
The above construction of prior art pressure regulators has a number of drawbacks. The pressure relief valve is generally fixed to the tubular stem and requires the diaphragm to be also perforated in the area of the tubular stem. Furthermore, the pressure relief valve is very small and thence relatively expensive and makes assembly more difficult, besides being itself a construction part.
The tubular stem requires a transverse hole to be formed therein for communication of the inside tubular space with the balance chamber.